Only three possible modes of procedure are available to protect a facility from direct lightning strokes. They are:
1. Eliminating the source of the stroke by discharging the thundercloud charge or the associated induced charge on the earth's surface.
2. Decreasing the electrostatic field caused by a thundercloud charge around the object to be protected by creating a space charge of the opposite polarity.
3. Providing a bypass path for lightning strokes, thereby preventing direct strokes into the facility.
Various lightning stroke protection devices are known. Some touch upon dissipative concepts and strike prevention. Those teachings include the following U. S. references:
______________________________________ 1) J. S. Barber 1,096 March 5, 1839 2) Chambers 234,173 November 9, 1880 3) Knudson 234,484 November 16, 1880 4) Newhall 250,950 December 13, 1881 5) Upton 315,679 April 14, 1885 6) Vail 357,050 February 1, 1887 7) Cage 1,743,526 January 14, 1930 8) Carpenter 4,180,698 December 25, 1979 9) Gillem 4,605,814 August 12, 1986 ______________________________________
A brief description of the relevant prior art is discussed below:
1. Barber -- A wood insulator holds a copper umbrella atop the facility. No conduction to ground is provided. Therefore, the effectiveness of this lightning rod is questionable.
2. Chambers -- A sealed oil/gas storage tank is affixed with two concentric circles of lightning rods. Short wires project both upwardly and downwardly from the concentric circles. However, the entire lightning rod assembly is insulated from the ground. Therefore, the effectiveness of this lightning rod is questionable.
3. Knudson -- An oil tank lightning rod and dissipation system uses water spray to reduce gas concentrations over the tank. The assembly is grounded to earth to serve as a lightning rod. Finally, the ground is saturated with water. This is an effective lightning protection system since it dissipates the charge from above the tank thereby offering stroke prevention. No attention to ionizer points is made.
4. Newhall -- Lightning protection for an oil tank is provided by mounting a pole atop the tank. The pole is insulated from the tank. The pole has a height equal to the radius of the tank. The pole supports a conductive tip and copper cables which are connected in an umbrella fashion to the ground. This is an effective lightning protection system since it dissipates the charge from above the tank. Additionally, a copper rod is coiled around the oil inlet and outlet pipes to prevent strokes that hit the pipes from reaching the tank.
Newhall describes prior art consisting of a series of poles erected around the tank. A wire network was formed connecting the tips of the poles. No attention to ionizer points is made.
5. Upton -- The primary lightning conductor taught by Upton is barbed wire. The barbs serve to dissipate the electricity into the air evenly along the wire in addition to the dissipation into the ground. Upton prefers all the barbs pointing in one direction away from the facility. A network of barbed wire is supported over the facility by poles. A short interval exists between short barbs. No attention to design dimensions is made.
6. Vail -- Overhead electric utility wires are protected by an independent strand of barbed wire hung over it and grounded. The ground wires are run down the utility poles and attached to underground copper plates. No attention to design dimensions is made.
7. Cage -- Cage deals with the conditions precedent to the flash for the purpose of preventing the flash itself. Cage prefers to surround the facility above and peripherally with a small diameter wire having sharp points. The sharp points tend to dissipate mounting charges into the atmosphere. Cage connects the wire network to the facility before grounding. Floats inside an oil tank may also be connected to the network.
Key to Cage's teaching is that the number of "barbs" in his wire is adequate to dissipate and transfer by ionization the total charge building up between the cloud and facility at least as fast as that charge tends to build up. Furthermore, the "barbs" in his wire are adequate to dissipate and transfer by ionization the total charge building up between the cloud and facility at least as fast as that charge tends to build up. Furthermore, the "barbs" must be spaced apart far enough so as to get little or no interference between their concentrated effects on the lines of force from the cloud. Cage's dissipating systems allow the charge differential between the cloud and earth to flow back to the cloud before the flashover point is reached.
Cage suggests a slightly wider spacing when parallel wires are used as opposed to single wires. Cage teaches greater dissipation rates at high elevations of the wire and "barbs". Therefore, multiple tall towers are recommended.
In summary, Cage teaches offering a large charge transferring area having multiple barbs to the charged cloud. However, no precise parameter designs are taught which maximize these basic teachings.
8. Carpenter - Carpenter teaches surrounding the facility with an underground current collector. This current collector diverts the ground charge up to an ionizer on a centralized tower in the center of the current collector. Carpenter stresses forming uniform field shapes over the facility, thus avoiding upward going leaders. Various estimates are provided for figuring facility area protection from varying shaped ionizer towers.
9. Gillem introduces a toroidal wire brush concept. This acts as the dissipative medium for high towers. Wires are packed at up to 250 per inch to act as ionizer points. However, no attention has been paid to the point interference phenomena first identified by Cage and refined by Carpenter. This has resulted in a series of failures (strokes to it).
Lightning protection-concepts may be divided into two categories, stroke collection/diversion and stroke prevention. The stroke collection/diversion systems are best typified by the conventional lightning rod systems. The lightning rod systems consist of an air terminal, a downconductor and a grounding system. Of the prior art previously listed. Barber, Chambers, Knudson and Newhall all deal with different forms of stroke collection and grounding concepts. They teach various forms of lightning rod systems. Vail teaches the use of conventional barbed wire for the creation of air ionization terminals for use with a lightning collections and grounding system.
Stroke prevention systems are those that prevent a stroke from terminating within the protected area or on the protecting system. These prevention systems are usually referred to as dissipative systems. Upton was the first to consider this concept. Only a gradient line exists between a lightning rod and a lightning dissipator. Even a single point lightning rod acts to some extent to dissipate a change to atmosphere before a lightning stroke, thus offering a small amount of prevention. Cage then refined the concept and explained some of the operational principles and identified some of the critical parameters. Cage did not define the parameter interrelationships. Carpenter developed one form of dissipating wire and a new charge collection concept. Carpenter expanded on the parameter interrelationships.
All of the aforementioned prior art identified concepts but did little toward presenting specific design parameters for the ionizer itself. Failures within the stroke prevention art pointed out the need for more specific design data.
The Dissipation Array System, subsequently referred to as DAS, is a true lightning stroke prevention system. The operational concept is presented within this disclosure.
Failures of the barbed wire based systems and certain dissipation wire systems pointed out the need to determine the required design parameters for each specific application. The barbed wire systems proved to be less than 60 percent effective. Carpenter's dissipation wire proved to be better than 99 percent effective. A study of DAS systems installed since Carpenter's 1979 patent revealed some inherent weaknesses in the early designs. Subsequent tests provided the data required to identify these weaknesses and produce an effective DAS.